The present invention relates to an angular velocity sensor, more particularly, relates to the angular velocity sensor employed for the attitude control and navigation of moving objects such as an airplane, an automobile, a robot, a ship, or other vehicles; for preventing still and vided cameras shake; and for the remote control for remotely operated equipment.
As an angular velocity sensor, the typical one is disclosed in Japanese Patent Non-examined Publication No. H10-170276 (the corresponding U.S. Pat. No. 5,945,599). The sensor has a mass portion as a vibrator and electrodes facing to the mass portion. In the structure, an electrostatic attraction generated between the electrodes vibrates the mass portion. When an angular velocity is applied to the mass portion, the Coriolis force developed at the mass portion acts in a direction at right angles to the axis of the applied velocity and to the vibrating direction of the mass portion. The Coriolis force displaces the mass portion, by which the distance between the facing electrodes changes. That is, a capacitance between the electrodes changes due to the displacement of the mass portion. Through the capacitance, the angular velocity sensor detects information on the angular velocity.
As another example of the prior-art sensor, Japanese Patent Non-examined Publication No. H11-26777 (the corresponding U.S. Pat. No. 6,028,332) discloses a semiconductor-type angular velocity sensor. In a beam structure similarly formed to the aforementioned type, a mass portion is driven by an electrostatic attraction. At this moment, a strain gauge disposed at the beam structure detects a displacement in the mass portion brought by the Coriolis force.
In the former example of the prior-art sensors described above, the angular velocity information is obtained from a change in capacitance between the oppositely disposed electrodes. In the latter example, the information is detected by the strain gauge disposed on a beam connected to the mass portion. The both ways are based on a displacement in the mass portion by the Coriolis force when the mass portion is vibrated.
With the ways above, however, the displacement component generated from the drive of the mass portion is partly mixed into the Coriolis force component. It is therefore difficult to extract a xe2x80x9cgenuinexe2x80x9d Coriolis force component from the mixture. In other words, the Coriolis force acting in a direction perpendicular to the vibrating mass portion is extremely smaller than the driving force on the mass portion. Therefore, it is hard to draw a distinction between vibration caused by the Coriolis force and vibration occurred in a direction different from the vibrating mass portion. Aforementioned problem has often hampered the sensor from detecting angular velocity with high accuracy.
In order to effectively drive the mass portion and the facing electrodes by electrostatic attraction, or monitor a change in a capacitance between the electrodes, the distance between the electrodes preferably ranges from 2-3 microns to 5-6 microns. However, due to an accidental intrusion of foreign matter or dust into the gap, there is a possibility of causing a short circuit between the electrodes. It causes a troublesome problem, in particular, in a structure having many electrodes formed into a comb shape for an effective drive or detectionxe2x80x94the drive by the electrostatic attraction or the detection of the capacitance has often ended in failure by a single short circuit between the electrodes due to the entry of foreign matter.
This may be an obstacle to mass-production of the angular velocity sensor with multiple electrodes.
It is therefore the object of the present invention to provide an angular velocity sensor not allowing other vibration components, in particular, driving displacement components to mix into the Coriolis force component.
The angular velocity sensor of the present invention contains a first through a fifth beams: the first, the second, and the third beams have a length of substantially the same and are disposed in a substantially parallel arrangement on a substantially the same planexe2x80x94with the first beam placed between the second and the third; the fourth connects each one end of the first through the third, while the fifth connects each other end of them. In addition, the mid-portion of the first beam is supportively fixed.
The first beam serves as a detector; the second serves as a driver; and the third serves as a monitor.
With the structure above, other vibration components are not allowed to mix into the Coriolis force component. Such a simply structured angular velocity sensor can thus detect the angular velocity with much accuracy.